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Gamma Cassiopeiae: spectrum

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About this observation
Observer
David Swan
Time of observation
18/01/2018 - 20:28
Object
Gamma Cassiopeiae
Observing location
Tynemouth, UK
Equipment
200mm SCT @ f/6.3
ASI178MM
Star Analyser
FireCapture and RSpec
Exposure
Stack of 100 x 100ms frames
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A very clear hydrogen alpha emission line from this well-known Be star.

Comments

allenhugh10's picture

That's very nice David!

djswan2002's picture

Thanks very much Hugh. Focusing is quite a challenge isn’t it? For example, I found that when I achieved a sharp tapering where the first order spec starts (in visible light of course!), the Halpha line for gamma cass wasn’t as clear as it was at a slightly different focus. What do you recommend? David

allenhugh10's picture

Hi David,

As I showed in the forum conversation I adjust the focus based on the Bahtinov mask pattern formed by the zero order star image. I experimented with adjusting the focus until I got the sharpest A-type star spectrum and then used the appearance of the Bahtinov mask image to act as a reference for future focus setting. I always set the focus to give the same Bahtinov pattern. Does that make sense?

Cheers

Hugh

Andy Wilson's picture

Great spectrum David! As well as the hydrogen emission you can also see absorption by the Earth's atmosphere, telluric lines, a good example between H-alpha and 7000 Angstroms.

djswan2002's picture

Thanks Hugh - I was a bit slow on the uptake, but get the idea now. A clever system. I might buy one of these masks soon.

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